SIP (Session Initiation Protocol) is defined by IETF (Internet Engineering Task Force) in RFC (Request for Comments) 3261 and has been developed to allow session control between peers. A session is also known as a call. SIP is typically used for initiating/setting up and tearing down/terminating multimedia communication sessions such as but not limited to voice and video calls etc over an IP bearer such as that provided by the Internet. SIP is a derivative of the HTTP (Hypertext Transfer Protocol) system, which is ASCII (American Standard Code for Information Interchange) based. SIP is intended to support a superset of the call processing functions present in the PSTN (Public Switched Telephone Network). Thus, SIP can be used for operations such as but not limited to call setups, call terminations, call modifications and call transfers etc. These operations can also be collectively known as SIP operations.
SIP SigComp (as per RFC 5049 Applying Signaling Compression (SigComp) to the Session Initiation Protocol) is a mechanism that uses a compression scheme to compress SIP strings thereby achieving a smaller payload. Compressed SIP strings are sent to the device and then de-compressed by the device.